[LeetCode] Add and Search Word

Design a data structure that supports the following two operations:

void addWord(word)
bool search(word)

search(word) can search a literal word or a regular expression string containing only letters a-z or .. A . means it can represent any one letter.

For example:

addWord("bad")
addWord("dad")
addWord("mad")
search("pad") -> false
search("bad") -> true
search(".ad") -> true
search("b..") -> true

Note:
You may assume that all words are consist of lowercase letters a-z.

字典树，注意匹配 '.' 的时候要对所有的子树进行匹配，这时就得用DFS了。

class WordDictionary {
private:
    struct trinode {
        trinode *ch[26];
        bool iskey;
        trinode(): iskey(false) {
            for (auto &a : ch) a = NULL;
        }
    };
    
    trinode *root;
    
    void _addWord(string s) {
        trinode *p = root;
        for (auto &a : s) {
            int idx = a - 'a';
            if (p->ch[idx] == NULL) p->ch[idx] = new trinode();
            p = p->ch[idx];
        }
        p->iskey = true;
    }
    
    bool _search(trinode *root, string s, int pos) {
        if (pos == s.length()) return root->iskey;
        if (s[pos] == '.') {
            for (auto &p : root->ch) {
                if (p != NULL && _search(p, s, pos + 1)) return true;
            }
            return false;
        } else {
            int idx = s[pos] - 'a';
            return (root->ch[idx] && _search(root->ch[idx], s, pos + 1));
        }
    }
    
public:
    WordDictionary() {
        root = new trinode();
    }
    // Adds a word into the data structure.
    void addWord(string word) {
        _addWord(word);
    }

    // Returns if the word is in the data structure. A word could
    // contain the dot character '.' to represent any one letter.
    bool search(string word) {
        return _search(root, word, 0);
    }
};

// Your WordDictionary object will be instantiated and called as such:
// WordDictionary wordDictionary;
// wordDictionary.addWord("word");
// wordDictionary.search("pattern");

 搜索的时候可以只有遇到 '.' 的时候才递归，否则就迭代。可以提高一点点效率。

    bool _search(trinode *root, string s, int pos) {
        if (pos == s.length()) return root->iskey;
        trinode *p = root;
        for (; pos < s.length(); ++pos) {
            if (s[pos] != '.') {
                int idx = s[pos] - 'a';
                if (p->ch[idx] == NULL) return false;
                p = p->ch[idx];
            } else {
                for (int idx = 0; idx < 26; ++idx) {
                    if (p->ch[idx] && __search(p->ch[idx], s, pos + 1)) return true;
                }
                return false;
            }
        }
        return p->iskey;
    }